Aiding a Better Understanding of Molybdopterin: Syntheses, Structures, and pKa Value Determinations of Varied Pterin-Derived Organic Scaffolds Including Oxygen, Sulfur and Phosphorus Bearing Substituents

Abstract

Abstract Multistep synthetic procedures were established for the preparation of a set of four compounds serving as models for aspects of molybdopterin (mpt), a unique ligand system in the active sites of molybdenum and tungsten dependent oxidoreductases. The synthesized compounds were investigated with various analytical techniques including single crystal X-ray structural determination and the measurement of the specific pKa values of all four compounds in the non-aqueous solvent acetonitrile, which range from 11.09 to 11.82. The obtained physico-chemical data supported by theoretical analysis indicate that even functional groups quite far away from the cofactor sites which are reactive can have an impact on characteristics which are important for the reactivity. The data were used to identify the likely protonation sites on the model compounds and thereby allow for a better understanding of molybdopterin s potential active role in transformations in the active sites of oxidoreductases in relation to specific functional groups of mpt with respect to protonation events and tautomerization.